The present invention relates to photographic printing systems. In particular, the present invention is a method and apparatus for correcting the output signals of light sensors used to measure optical characteristics of photographic film to be printed.
Photographic printers produce color or black and white prints or transparencies from photographic film originals (generally negatives). High intensity light is passed through the film and imaged on the photosensitive print medium (film or paper). The photographic emulsion layer on the print paper or film is exposed and subsequently processed to produce a print or transparency of the scene contained in the original.
Automatic photographic printers often include an automatic density correction (ADC), or color or density scanning mechanism, which scans the negative prior to printing and provides measurements of the transmission density of the negative at defined discrete or continuous areas, as opposed to an average or integrated measurement over the entire negative. The measurements of the negative so derived can be used as the sole means of exposure determination, or in conjunction with other measurements to calculate the proper exposure. Many of the scanning systems have included moving optical elements to provide the desired scanning, while other scanning systems may have used fixed sensors which view different portions of the negative. A system having fixed sensors rather than moving optical elements is generally desirable from a cost, size, and reliability standpoint.